A video signal to be displayed on a display device comprising a set of pixels includes a succession of frames to be displayed each comprising a set of points, each point being associated with one pixel of the screen. The frames to be displayed succeed one another at a rate of around 60 frames/s. Each point is characterized by a luminance defined for example in a format known as RGB (for Red Green Blue) by a binary word (of 24 bits for example) comprising three binary numbers (of 8 bits for example), each corresponding to a luminance value for the three basic colors Red, Green and Blue.
On such a display device, one known problem is the appearance of flashes during a change of frame. These flashes result from significant variations in the luminance of one and the same point from one frame to the next with respect to the luminance of an adjacent point. A white flash appears when the luminance of a point increases significantly from one frame to the other. Conversely, a black flash appears when the luminance of a point decreases significantly from one frame to the other. The appearance of flashes is due at least partly to the difference between the rise time and the fall time of the luminance of a pixel of the screen. The rise time is the time taken by the luminance of a pixel to pass from a first value to a second value greater than the first. Conversely, the fall time is the time taken by the luminance of a pixel to pass from a first value to a second value lower than the first. The rise time and the fall time depend in particular on the type of LCD pixel, on the variations caused by the process of manufacturing the display device, on the magnitude of the jump in luminance (difference between the first luminance value and the second luminance value) to be carried out, on the temperature, on the viewing angle, and other factors.
This problem is particularly disruptive for applications in which the images to be displayed consist essentially of very small objects of one color and/or a very different luminance of a background color of the screen, such as images supplied by a sonar system for example.
Several techniques are envisaged for solving this problem. International Publication No. WO 2007/123628 A1 proposes a technique which consists in inserting, between two frames of a video signal, one or more intermediate frames in which the luminance of the pixels is calculated by a weighted sum of the luminance of the corresponding pixels in the preceding frame and of the luminance of the corresponding pixels in the subsequent frame. The run rate of the frames is thus doubled. The technique of the '628 published application is implemented in the form of a software item which is executed inside a video controller located upstream of a display device.